Because of increasingly stringent legal requirements on the maximum allowable toxic content of the exhaust gas of internal combustion engines, but also from the standpoint of improving the ride in motor vehicles, electronic control units are used with increasing frequency for controlling various engine parameters. For instance, it is known to calculate the fuel requirement electronically from the aspirated air quantity or air flow rate, or from the pressure in the intake tube and the engine speed, and then to trigger an injection apparatus with a corresponding trigger signal. In full-load operation, however, the intake strokes sometimes cause such major pulsations of the air quantity flow rate signal and hence of the load signal, which may be in the form of an injection duration or a fuel quantity signal, that the mixture composition fluctuates, which is disruptive and causes increased toxic emissions. In engine idling, and in particular in overrunning or engine braking in the idling speed range, the phase displacement between the air quantity or engine speed detection, the injection instant and the torque output also becomes preceptable and is often disruptive. Rough engine idling, and engine "bucking" in overrunning, are the result.
German Patent Disclosure Document DE-OS 24 55 482 describes an arrangement for obtaining signals from which trigger signals for the fuel metering are generated in an electronic control unit. The signals serving as input signals for the control unit and relating to engine speed and aspirated air flow rate are supplied to a rectifier having a low-pass filter characteristic, in order to damp any alternating voltage components that may be present and that can arise from factors external to the operation. Since the low-pass filter characteristic of the rectifier remains fixed, or in other words is not adapted to changing engine states, the arrangement does not always function completely satisfactorily. Above all, when there are sudden load changes, filter-dictated delays in fuel metering occur.